Sarcocheilichthys hainanensis Nichols & Pope, 1927

(Figs 1, 4–7)

Sarcocheilichthys hainanensis Nichols & Pope, 1927: 352, Fig. 21, Pl. 26 (fig. 3)

(holotype: AMNH 8370,

Nodoa, Hainan Island, China); Chevey & Lemasson, 1937: 44; Kottelat 2001: 39; Kottelat 2001: 79; Kottelat 2013: 158; An et al. 2020: 217

Sarcocheilichthys nigripinnis hainanensis: Bănărescu & Nalbant 1967; Yu 1986.

Materials Examined. NTOUP-2013-05-026, 3 specimens, 50.80–85.14 mm SL; Baisha County, Hainan Island. PRC; coll. I-S. Chen et al., 26 May 2013.

Diagnosis. The Hainan rainbow gudgeon Sarcocheilichthys hainanensis can be distinguished from its congeners by the following unique combination of characters: (1) fin rays: D 3+7; A 3+6; P 1 1+14; P 2 1+7; (2) scales: LL 39– 40; TR 8; PreD 11; (3) vertebral count 4+33; (4) body feathers: body overall slender; pharyngeal teeth in 1 row; lip lobes bulb-like; barbles absent; male individuals with a finger-like protrusion posterior to anus; and (5) coloration: body with a lateral streak posterior from gill slits to caudal fin base; dorsal fin with a single black streak and black blotch; upper and lower caudal fin edges with single black streaks.

Redescription. Body proportions as shown in Table 1, frequencies of meristic counts in Table 2. Body spindle-shaped, depth greatest at dorsal fin base. Body profile slightly convex anterior to dorsal fin base and slightly concave posterior towards caudal peduncle base. Snout bluntly, large male individual with a slight concave. Mouth inferiorly positioned; upper jaw prominent, posterior end of gape doesn’t reach beyond middle-vertical position of orbit; both jaws retractable, outstretching downward. Upper lip thick; tip of lower lip with thin horny sheath. Pharyngeal teeth in one row. Lower lip with two lateral lobes (Fig. 4B), short and bulb-like, situated along lower jaw, anterior end pointing towards tip of lower jaw, connecting to upper lip posteriorly. Barbles absent. Male individuals with a short, finger-like extension just posterior to anus (Fig. 7C). Vertebrae 4+33.

Fins. Dorsal fin with 3 unbranched rays and 7 branched rays (3); anal fin with 3 unbranched rays and 6 branched rays (3); pectoral fins with 1 unbranched ray and 14 branched rays (3); pelvic fins with 1 unbranched ray and 7 branched rays (3). All fins flexible. Dorsal fin origin anterior to pelvic fin insertions. Pectoral fins horizontal, slightly longer in length than head, posterior tips not extending beyond pelvic fin insertions. Posterior tip of pelvic fins extending beyond anus when compressed. Caudal fin forked, upper and lower lobes equal in length and shape. All fins without elongated rays.

Squamation. Lateral line pored scales 39 (3); transverse scale rows 8 (3); predorsal scales 11 (2) or 12 (1). All scales cycloid, moderately big, no exceptionally enlarged scales. Head completely naked, predorsal regions scaled until vertical position of upper edge of gill slit. Thoracic region and abdomen scaled; anus almost covered by scales. Lateral line complete.

Coloration in preservatives. Body yellow (caused by long-term preservation), dorsal side of body dark above lateral line (dark regions restricted in dorsal side of body in juveniles), and blotchless below lateral line. Body with a thick lateral streak from gill slits to caudal fin base, width about three rows of scales. Head yellowish with dorsal side black until lower rim of orbit, ventral side and thoracic region weakly pigmented. A black, slight oval-shaped spot just posterior to opercle with upper end below lateral line (Fig. 6B). Dorsal fin with a broad stripe along unbranched rays and a single blotch located at median-posterior part (Fig. 5B). Pectoral fins, pelvic fins and anal fin with black shade or vague blotches between branched rays. Both lobes of caudal fin with a broad black smear located at upper and lower edges.

Remarks. The Hainan rainbow gudgeon Sarcocheilichthys hainanensis can be differentiated from its Chinese congeneric species, S. sinensis and S. lacustris, by its broad mid-lateral stripe (vs. having broad transverse bands), and from S. sciistius, S. parvus, and S. caobangensis by its mid-lateral stripe not extending anteriorly to snout tip across orbit (vs. stripe extending to snout tip). S. hainanensis can also be differentiated from S. nigripinnis and S. davidi in having only one row of pharyngeal teeth (vs. both having two rows), and further separated from the former in having a finger-like protrusion posterior to the anus in male individuals (vs. no such character), dorsal fin markings (single stripe and a posterior blotch vs. weakly pigmented), smaller head (18.26% in SL vs. 20.17% in SL), and smaller caudal peduncle depth (11.83% in SL vs. 13.31% in SL) (see Table 1).

Distribution. Sarcocheilichthys hainanensis has been known so far only from Hainan Island, PRC.